intermittent data, or a single signal
transmission from a sensor or input
device. Applications include simple
two-way robot control, traffic
management systems, and other
consumer and industrial equipment
that requires short-range wireless
transfer of data at relatively low rates.
The technology defined by the ZigBee
specification is intended to be simpler
and less expensive than other WPANs,
such as Bluetooth.

ZigBee operates in the industrial,
scientific, and medical (ISM) radio
bands of 915 MHz in the USA and
Australia, and 2. 4 GHz in most other
areas worldwide. Data transmission
rates vary from 20 to 900
kilobits/second. I recently
received some XBee S2B Pro
modules (Figure 8) and I
quickly hooked them up for a
test. I was communicating with
the XStick ZB AT USB dongle
(shown in Figure 9) on my
laptop. I was hoping for a bit
more range, but the dongle is
low power — just a bit over 2
m W — and I had a bit of
trouble with longer range due
to the small, internal antenna.

I used an old spectrum
analyzer to look at the 2. 4 GHz
signal, but it was gone by the
time I brought the wireless test
board with the XBee module
attached down to my garage.
The dongle receiver does have
a sensitivity of -90 dBm — not too bad
for such a small device.

Final Thoughts

There are many more varieties of
RF and control links that have been
used by robot experimenters. Wi-Fi
(that uses the IEEE 802.11 standard)
has been used for robot control,
though we mostly use this RF
technology for a close proximity PC
network. It has its security problems,
but is fine for robot use. Bluetooth —
operating in the 2. 4 to 2. 48 GHz band
There really is no limit to
the methods that can be used
to control a computer, or even
a robot. Figure 11 shows a
computer application that
can easily be converted to
robot control. These glasses
developed at the Imperial
College in England allow
a disabled person to control
a computer with just their
eyes. Just think of the
possibilities! SV

FIGURE 11. GT3D device can control a computer
or robot through eye commands.